Phoenix is one of the most unusual Animals we've ever had in Charm Farm - When they were first introduced - you place it as a baby Phoenix and as it grows it turns into a Pile of Ashes, sell the Ashes and another Phoenix would land in your inventory! He literally rose from the Ashes, like a proper Phoenix should!

Now that the quest timer has expired, when you place your Phoenix he will be ashes and then grow into an adult Phoenix. If you sell him he will not give you another. He's just gone for good.